It didn't help them much that they had superior ports when the comp had lessor ports plus games the GC didn't have. As a system, I preferred Cube over PS2 and Xbox. Games is where they took a beating though. You got a PS2 for the game library and your second system was an Xbox if you played online, or a Gamecube if you didn't care for that. Not too many people fall into the latter, and fewer still had all three. The software libraries all around was very me-too and same-ish, too much so to warrant that.
There wasn't anything particularly flawed with it. It was just the weakest shower in that environment. It had more potential than the rest, but actualized the least. It could be considered the Dreamcast's second-cousin, almost.